Atomic force microscopy investigation of the surface topography and adhesion of nickel nanoparticles to submicrospherical silica

Surface topography and the adhesion of amorphous and polycrystalline nickel nanoparticles on the surface of silica submicrospheres (200-250 nm) were probed by atomic force microscopy (AFM). Probe areas down to 50×50 nm in dimension were scanned on a single submicrosphere immobilized in a thermoplastic resin bed. The rough surface of the silica submicrospheres at higher resolution may arise from secondary silica particles which constitute the submicrospheres. Nickel particles were deposited on the submicrospheres by a sonochemical method. Amorphous nickel particles formed by the aggregation of nickel clusters were soft, experienced poor adhesion to the silica and caused huge tip-induced particle movements. But polycrystalline nickel nanoparticles in the size range of 20-30 nm were hard and strongly adhered to the silica. The stronger adhesion of polycrystalline nickel is explained in terms of a silicate-type impurity phase formed in the nickel-silica interface during crystallization.